Electrolyte containing polyheterocyclic organophosphorus compound and lithium ion battery

Abstract

The application discloses an electrolyte containing a multi-heterocyclic organic phosphorus compound, which comprises a main lithium salt and a nonaqueous solvent, and further comprises a first additive, which is a multi-heterocyclic organic phosphorus compound shown in the following formula (I): wherein each substituent is described in the description; and a second additive, which is selected from a boron trifluoride complex. The electrolyte provided by the application can significantly improve the high-temperature cycle performance of a lithium ion battery and reduce high-temperature storage gas production through the synergistic effect of the multi-heterocyclic organic phosphorus compound and the boron trifluoride complex.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion battery electrolyte, in particular to a kind of electrolyte containing multi-heterocyclic organic phosphorus compound and lithium ion battery. BACKGROUND

[0002] Lithium ion battery is widely used in smart phones, notebook computers, unmanned aerial vehicles, electric vehicles and other fields due to its high energy density, long cycle life, good safety performance and environmental friendliness. With the increasingly wide application of lithium ion batteries, people's requirements for the performance of lithium ion batteries are also increasing.

[0003] To meet the demand of people for the service life and range of electric vehicles, developing lithium ion batteries with high energy density and long cycle life is the focus of research in recent years. For ternary materials, increasing the charging upper limit voltage of the battery and increasing the content of nickel in the ternary material are common means to improve the energy density of the battery. However, with the increase of the upper limit of charging voltage and the content of nickel, the instability of the material is aggravated, which will bring many problems, such as irreversible phase transition of the positive electrode material, aggravation of transition metal dissolution and electrolyte decomposition gas, etc., which seriously affect the comprehensive performance of lithium ion battery.

[0004] At present, developing new electrolyte additives or inhibiting the internal side reactions of the battery through the synergistic effect between different additive compositions to optimize the electrode interfacial film is one of the main ways to improve the performance of lithium ion battery. SUMMARY

[0005] In order to solve the above technical problems, the present application provides an electrolyte capable of improving the high-temperature cycle performance and high-temperature storage performance of lithium ion battery at high voltage.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] An electrolyte containing a multi-heterocyclic organic phosphorus compound, comprising a main lithium salt and a non-aqueous solvent, wherein the electrolyte further comprises:

[0008] A first additive, which is a multi-heterocyclic organic phosphorus compound represented by the following formula (I):

[0009]

[0010] In the formula, G1, G2 and G3 are independently selected from furan ring, thiophene ring, pyridine ring, pyrazine ring, pyridazine ring or s-triazine ring; Xn represents that G1, G2 and G3 rings are independently substituted by n X substituents, wherein X is selected from hydrogen, halogen, cyano, sulfonyloxy, sulfonyl, C 1-12 alkyl, C 1-12 alkoxy, C 2-12 ester, C 2-12alkyl, C 6-16 aryl, C 6-16 aryloxy, and C 1-12 alkyl, C 1-12 alkoxy, C 2-12 ester, C 2-12 alkenyl, C 6-16 aryl, or C 6-16 aryloxy; n is an integer from 1 to 4; the X substituents on the same ring can be the same or different, and the X substituents on different rings can be the same or different.

[0011] a second additive, the second additive being a boron trifluoride complex.

[0012] As a preference, in the formula, X is selected from the group consisting of hydrogen, halogen, cyano, sulfonyloxy, sulfonyl, C 1-6 alkyl, C 1-6 alkoxy, C 2-6 ester, C 2-6 alkenyl; n is an integer from 2 to 4.

[0013] More preferably, X is selected from the group consisting of hydrogen, methyl, fluorine.

[0014] Most preferably, the first additive is selected from at least one of the following formulae:

[0015]

[0016] Further, the boron trifluoride complex is selected from at least one of the group consisting of boron trifluoride carbonate complex, boron trifluoride carboxylate complex, boron trifluoride ether complex, boron trifluoride nitrogen heterocycle complex, boron trifluoride sulfone complex. Among them, the boron trifluoride carbonate complex includes boron trifluoride chain carbonate complex, boron trifluoride cyclic carbonate complex; the boron trifluoride nitrogen heterocycle complex includes boron trifluoride pyridine complex, boron trifluoride pyrrole complex.

[0017] As a preference, the boron trifluoride complex is selected from at least one of the following formulae:

[0018]

[0019] When the first additive and the second additive of the present application exist simultaneously in the electrolyte system, the trifluoroboron can react with the heterocycle in the polyheterocyclic organic phosphine compound, and it is speculated that it can induce a small amount of polymer to be generated in the system at high temperature, covering the electrode surface, improving the isolation effect of the electrode on the electrolyte, and inhibiting the decomposition reaction of the electrolyte on the electrode; at the same time, the polyheterocyclic organic phosphine compound as a common organic ligand can complex with transition metals to form a complex at high temperature, inhibiting the deposition of metal ions on the electrode surface; the effects of the two aspects together improve the high-temperature performance of the lithium ion battery.

[0020] Generally, the first additive and the second additive can play a synergistic effect when they exist simultaneously, but the amount of the two is different, and the synergistic effect is different. As preferred, the first additive accounts for 0.1-5.0% of the total mass of the electrolyte, and the second additive accounts for 0.3-10.0% of the total mass of the electrolyte. More preferably, the first additive accounts for 0.3-3.0% of the total mass of the electrolyte, and the second additive accounts for 0.5-4.0% of the total mass of the electrolyte.

[0021] In the electrolyte of the present application, the main lithium salt can be selected from the commonly used lithium salt in the electrolyte. As preferred, the main lithium salt is selected from at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium tetrafluoro oxalate phosphate, lithium bis-trifluoromethanesulfonimide, lithium bisfluorosulfonimide, lithium bisoxalate borate, and lithium difluoroxalate borate, preferably at least one of lithium hexafluorophosphate and lithium bisfluorosulfonimide, and the mass percentage of the main lithium salt in the electrolyte is 7.0-20.0%. As preferred, the main lithium salt is selected from at least one of lithium hexafluorophosphate and lithium bisfluorosulfonimide, and the mass percentage in the electrolyte is 10.0-15.0%.

[0022] In the electrolyte of the present application, the non-aqueous solvent can be selected from the commonly used solvent in the electrolyte. As preferred, the non-aqueous solvent is selected from at least one of ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, vinylene carbonate, fluoroethylene carbonate, 1,4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, and ethyl butyrate.

[0023] In order to further improve the comprehensive performance of the electrolyte, the electrolyte further comprises a third additive, and the third additive is at least one selected from vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl sulfate, methane disulfonic acid methylene, 1,3-propane sulfonate lactone, 1,3-propylene sulfonate lactone, tris (trimethylsilyl) phosphite, lithium difluorophosphate, and the third additive accounts for 0.5-5.0% of the total mass of the electrolyte. More preferably, the third additive accounts for 0.8-3.0% of the total mass of the electrolyte.

[0024] The application further provides a lithium ion battery, which comprises a positive electrode sheet, a negative electrode sheet, a diaphragm arranged between the positive electrode sheet and the negative electrode sheet, and the electrolyte described in any one of the above.

[0025] Compared with the prior art, the application has the beneficial effects that:

[0026] The application can inhibit the side reaction in the battery under high voltage and high temperature conditions, reduce the dissolution of transition metals, and further improve the high-temperature cycle performance and high-temperature storage performance of the lithium ion battery through the synergistic effect of the multi-heterocyclic organic phosphorus compound and the boron trifluoride complex. DETAILED DESCRIPTION

[0027] The application will be further described below in conjunction with specific embodiments, but the application will not be limited to these specific embodiments. Those skilled in the art should recognize that the application covers all alternatives, improvements and equivalents included in the scope of the claims.

[0028] I. Preparation of electrolyte

[0029] Example 1

[0030] The example provides an electrolyte containing a multi-heterocyclic organic phosphorus compound, and the electrolyte is prepared by the following steps:

[0031] S1. In an argon-filled glove box, ethylene carbonate (EC) and methyl ethyl carbonate (EMC) are uniformly mixed in a mass ratio of 3:7 to obtain a mixed non-aqueous solvent;

[0032] S2. Dry LiPF6 is dissolved in the non-aqueous solvent to configure a 12.4%wt LiPF6 solution as a base electrolyte;

[0033] S3. 0.5%wt of I-1, 1.0%wt of II-1 and 1.0%wt of vinylene carbonate (VC) are added to the above base electrolyte to obtain the electrolyte of the example.

[0034] Example 2

[0035] The procedure of this example is the same as example 1, with the difference that in step S3, 0.5%wt of I-1, 1.0%wt of II-4 and 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte, obtaining the electrolyte of this example.

[0036] Example 3

[0037] The procedure of this example is the same as example 1, with the difference that in step S3, 0.5%wt of I-1, 1.0%wt of II-5 and 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte, obtaining the electrolyte of this example.

[0038] Example 4

[0039] The procedure of this example is the same as example 1, with the difference that in step S3, 0.1%wt of I-1, 1.0%wt of II-1 and 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte, obtaining the electrolyte of this example.

[0040] Example 5

[0041] The procedure of this example is the same as example 1, with the difference that in step S3, 2.0%wt of I-1, 1.0%wt of II-1 and 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte, obtaining the electrolyte of this example.

[0042] Example 6

[0043] The procedure of this example is the same as example 1, with the difference that in step S3, 4.0%wt of I-1, 1.0%wt of II-1 and 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte, obtaining the electrolyte of this example.

[0044] Example 7

[0045] The procedure of this example is the same as example 1, with the difference that in step S3, 0.5%wt of I-2, 1.0%wt of II-1 and 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte, obtaining the electrolyte of this example.

[0046] Example 8

[0047] The procedure of this example is the same as example 1, with the difference that in step S3, 0.5%wt of I-2, 1.0%wt of II-4 and 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte, obtaining the electrolyte of this example.

[0048] Example 9

[0049] The procedure of this example is the same as example 1, except that in step S3, 0.5%wt of I-2, 1.0%wt of II-5 and 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte, to obtain the electrolyte of this example.

[0050] Example 10

[0051] The procedure of this example is the same as example 1, except that in step S3, 0.5%wt of I-1, 0.3%wt of II-1 and 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte, to obtain the electrolyte of this example.

[0052] Example 11

[0053] The procedure of this example is the same as example 1, except that in step S3, 0.5%wt of I-1, 4.0%wt of II-1 and 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte, to obtain the electrolyte of this example.

[0054] Example 12

[0055] The procedure of this example is the same as example 1, except that in step S3, 0.5%wt of I-1, 8.0%wt of II-1 and 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte, to obtain the electrolyte of this example.

[0056] Comparative Example 1

[0057] The procedure of this example is the same as example 1, except that in step S3, 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte, to obtain the electrolyte of this example.

[0058] Comparative Example 2

[0059] The procedure of this example is the same as example 1, except that in step S3, 0.5%wt of I-1 and 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte, to obtain the electrolyte of this example.

[0060] Comparative Example 3

[0061] The procedure of this example is the same as example 1, except that in step S3, 0.5%wt of I-2 and 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte, to obtain the electrolyte of this example.

[0062] Comparative Example 4

[0063] The operation of the present comparative example is the same as that of Example 1, except that in the S3 step, 1.0%wt of II-1 and 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte to obtain the electrolyte of the present comparative example.

[0064] Comparative Example 5

[0065] The operation of the present comparative example is the same as that of Example 1, except that in the S3 step, 1.0%wt of II-4 and 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte to obtain the electrolyte of the present comparative example.

[0066] Comparative Example 6

[0067] The operation of the present comparative example is the same as that of Example 1, except that in the S3 step, 1.0%wt of II-5 and 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte to obtain the electrolyte of the present comparative example.

[0068] Comparative Example 7

[0069] The operation of the present comparative example is the same as that of Example 1, except that in the S3 step, 0.5%wt of I-1, 1.0%wt of pyridine and 1.0%wt of vinylene carbonate (VC) are added to the base electrolyte to obtain the electrolyte of the present comparative example.

[0070] II. Battery production and performance test

[0071] The electrolytes prepared in the above examples and comparative examples are respectively injected into lithium ion batteries, and performance tests are carried out. The lithium ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte and battery accessories, the positive electrode active material is LiNi 0.73 Co 0.07 Mn 0.2O2 , and the negative electrode active material is graphite. The battery preparation process is as follows:

[0072] The positive electrode active material lithium nickel-cobalt-manganese ternary material, the conductive agent and the binder polyvinylidene fluoride are mixed in a weight ratio of lithium nickel-manganese-cobalt ternary material: conductive agent: polyvinylidene fluoride = 97.3: 1.5: 1.2, a solvent N-methyl pyrrolidone is added, and after sufficient stirring and mixing, a uniform positive electrode slurry is formed; the slurry is coated on the positive electrode current collector aluminum foil, and then dried, rolled, cut and die cut to obtain the positive electrode sheet.

[0073] The negative active material graphite, conductive agent, binder styrene butadiene rubber, thickening agent sodium carboxymethyl cellulose are mixed according to the weight ratio of graphite: conductive agent: styrene butadiene rubber: sodium carboxymethyl cellulose = 96.4: 0.6: 1.8: 1.2, after adding deionized water, fully stirring, obtaining a uniform negative electrode slurry; the slurry is coated on the negative electrode current collector copper foil, then dried, rolled and cut, and the negative electrode sheet is obtained by die cutting.

[0074] The negative electrode sheet, the separator, and the positive electrode sheet are stacked in order, and the separator is placed between the positive and negative electrodes to isolate them. The bare battery cell is obtained by stacking the sheets one by one. After the bare battery cell is assembled, baked, and qualified for moisture, the above electrolyte is injected into the battery cell, and then the battery is obtained by the processes of soaking, formation, packaging, and capacity distribution.

[0075] The performance test method used is as follows:

[0076] (1) 45℃ high temperature cycle performance test: in a 45℃ constant temperature oven, the battery after capacity distribution is charged to 4.35V at 1C constant current and constant voltage, the cutoff current is 0.05C, and the battery is rested for 10min, and then discharged to 2.8V at 1C; after 500 cycles according to the above steps, the capacity retention rate after the 500th cycle is calculated:

[0077] The capacity retention rate after 500 cycles (%) = (the discharge capacity of the 500th cycle / the discharge capacity of the first cycle) * 100%.

[0078] (2) 60℃ high temperature storage for 30 days volume expansion rate test: in a 25℃ environment, the battery is discharged to 2.8V at 0.5C constant current, rested for 10min, and then charged to 4.35V at 1C constant current and constant voltage, the cutoff current is 0.05C. After resting at room temperature for 5h, the initial volume V1 of the lithium ion battery is measured by the drainage method. After 30 days of storage at 60℃, the volume V2 of the lithium ion battery after high temperature storage is measured by the drainage method.

[0079] The volume change rate of the lithium ion battery after high temperature storage (%) = (the volume V2 of the lithium ion battery after high temperature storage-the volume V1 of the lithium ion battery before high temperature storage) / the volume V1 of the lithium ion battery before high temperature storage * 100%.

[0080] The performance test results are shown in Table 1 below:

[0081] Table 1 Performance test results

[0082]

[0083]

[0084] According to the test results of Example 1, Example 4-6 in Table 1 above, it can be seen that when the amount of the multi-heterocyclic organic phosphorus compound is too much or too little, the high-temperature cycle performance of the battery will deteriorate, which may be due to the fact that too much multi-heterocyclic organic phosphorus compound leads to too large impedance of the system, and too little leads to insufficient film formation on the surface of the electrode, causing the high-temperature cycle performance to deteriorate. Therefore, when the amount of the multi-heterocyclic organic phosphorus compound is about 0.5%, the battery performance is best. According to the test results of Example 1, Example 10-12, it can be seen that when the content of boron trifluoride complex is too high, it will cause the system to produce gas seriously, and when the content is too low, it cannot form a film well on the electrode interface, and cannot improve the high-temperature cycle performance of the battery well. Therefore, when the amount of boron trifluoride complex is about 1.0%, the battery performance is best.

[0085] According to the electrical performance test results in Table 1 above, the multi-heterocyclic organic phosphorus compound can effectively inhibit the gas production during the 60°C storage of the battery, while the boron trifluoride complex does not have obvious effect on inhibiting gas production, and even becomes worse (Comparative Example 5). When the multi-heterocyclic organic phosphorus compound and the boron trifluoride complex are used alone, both can improve the 45°C cycle performance of the battery, but the effect is not obvious. However, when the two are used together, they can effectively inhibit the gas production during high-temperature storage, and greatly improve the 45°C cycle performance of the battery. According to the electrical performance test results of Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 7, it can be seen that the combination of the multi-heterocyclic organic phosphorus compound and pyridine does not have as good effect on improving the high-temperature performance as the combination of the multi-heterocyclic organic phosphorus compound and the boron trifluoride pyridine complex, indicating that the main part of the boron trifluoride pyridine complex that plays a role is boron trifluoride.

Claims

1. An electrolyte containing a polyheterocyclic organophosphorus compound, comprising a main lithium salt, a nonaqueous solvent, characterized in that: The electrolyte further comprises: a first additive, which is a multi-heterocyclic organic phosphorus compound represented by the following formula (I): wherein G1, G2, G3are independently selected from a furan ring, a thiophene ring, a pyridine ring, a pyrazine ring, a pyridazine ring, or a s-triazine ring; Xnrepresents that G1, G2, G3rings are independently substituted by n X, wherein X is selected from hydrogen, halogen, cyano, sulfoxy, sulfonyl, C 1-12 alkyl, C 1-12 alkoxy, C 2-12 ester, C 2-12 alkenyl, C 6-16 aryl, C 6-16 aryloxy, and C 1-12 alkyl substituted by halogen, sulfoxy, or sulfonyl, C 1-12 alkoxy, C 2-12 ester, C 2-12 alkenyl, C 6-16 aryl, or C 6-16 aryloxy; n is an integer from 1 to 4; a second additive, which is a boron trifluoride complex selected from at least one of a boron trifluoride carbonate complex, a boron trifluoride carboxylate complex, a boron trifluoride ether complex, a boron trifluoride nitrogen heterocycle complex, and a boron trifluoride sulfone complex.

2. The electrolyte solution containing a polyheterocyclic organic phosphorus compound according to claim 1, characterized by: X is selected from the group consisting of hydrogen, halogen, cyano, sulfonyloxy, sulfonyl, C 1-6 alkyl, C 1-6 alkoxy, C 2-6 ester, C 2-6 alkenyl; n is an integer from 2 to 4.

3. The electrolyte solution containing a polyheterocyclic organophosphorus compound according to claim 2, characterized by: X is selected from hydrogen, methyl, and fluorine.

4. The electrolyte solution containing a polyheterocyclic organophosphorus compound according to claim 3, characterized by: The first additive is selected from at least one of the following structures:

5. The electrolyte solution containing a polyheterocyclic organophosphorus compound according to claim 1, characterized by: The boron trifluoride carbonate complex includes a boron trifluoride chain carbonate complex and a boron trifluoride cyclic carbonate complex; the boron trifluoride nitrogen heterocycle complex includes a boron trifluoride pyridine complex and a boron trifluoride pyrrole complex.

6. The electrolyte solution containing a polyheterocyclic organophosphorus compound according to claim 5, characterized by: The boron trifluoride complex is selected from at least one of the following structures:

7. The electrolyte containing polyheterocyclic organophosphorus compound according to any one of claims 1 to 6, characterized in that: The first additive accounts for 0.1-5.0% of the total mass of the electrolyte; and the second additive accounts for 0.3-10.0% of the total mass of the electrolyte.

8. The electrolyte containing polyheterocyclic organophosphorus compound according to any one of claims 1 to 6, characterized by: The first additive accounts for 0.3-3.0% of the total mass of the electrolyte; and the second additive accounts for 0.5-4.0% of the total mass of the electrolyte.

9. The electrolyte solution containing polyheterocyclic organophosphorus compounds according to claim 1, characterized by that: The main lithium salt is selected from at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium tetrafluoro oxalate phosphate, lithium bis-trifluoromethanesulfonimide, lithium bisfluorosulfonylimide, lithium bisoxalate borate, and lithium difluorooxalate borate; and the main lithium salt accounts for 7.0-20.0% of the mass percentage of the electrolyte.

10. The electrolyte solution containing a polyheterocyclic organophosphorus compound according to claim 9, characterized by: The main lithium salt is selected from at least one of lithium hexafluorophosphate and lithium bisfluorosulfonylimide.

11. The electrolyte solution containing a polyheterocyclic organic phosphorus compound according to claim 1, characterized by: The non-aqueous solvent is selected from at least one of ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, and ethyl butyrate.

12. The electrolyte solution containing polyheterocyclic organophosphorus compounds according to claim 1, characterized by that: The electrolyte further comprises a third additive selected from at least one of vinylene carbonate, fluoro-vinylene carbonate, vinyl ethylene carbonate, vinyl sulfate, methane disulfonate methylene, 1,3-propane sulfonate lactone, 1,3-propylene sulfonate lactone, tris(trimethylsilyl) phosphite, and lithium difluorophosphate.

13. A lithium ion battery comprising a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet, characterized by: The lithium ion battery further comprises the electrolyte of any one of claims 1-12.

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